The present invention relates to single use disposable hypodermic syringes of uncomplicated construction to enable low cost mass production.
With the current medical knowledge of the danger of transmitting disease by use of un-hygenic hypodermic syringes, considerable efforts have been taken to provide a disposable syringe which after use is rendered inoperable and consequently cannot be used for a second time.
One set of proposals has been to provide a lance-like member on the leading edge of the hypodermic piston plunger so that on delivery of medication the lance pierces the front end wall of the syringe, thus rendering the syringe useless.
Another set of proposals has been to introduce a capturing chamber at the front end of the inside of the syringe barrel such that on delivery of medication the syringe piston is trapped within the barrel and any attempt to retract the piston causes the syringe to fail structurally and become unusable.
A third proposal, for use with cartridge packaged medication, has been to render the drive piston of the syringe non-retractable by including on it a resilient disc-like element or, in another such proposal, a plurality of short, stiff, flexible spikes are attached to the piston so as to project outwardly at an oblique angle and engage the inside of the tubular body of the syringe and allow very little retraction of the piston.
All the previous proposals have had limitations in that they are either workable only with cartridge loaded or pre-filled syringes, or could be subject to some form of tampering.
A major drawback with all non-cartridge type syringes is that they have not been "auto-distruct" at the beginning of the delivery stroke.